The present invention relates generally to spacecraft, and more particularly, to a spacecraft antenna storage and deployment system for use with a spacecraft antenna having a main reflector and a subreflector.
The assignee of the present invention manufactures and deploys communication spacecraft. Such spacecraft have antennas stowed thereon that are deployed once the spacecraft is in orbit. The antennas are used for communication purposes.
A number of deployable antennas have been developed in the past. Many of them are for use in ground-based vehicular applications. For instance, the Winegard Company has patented a variety of deployable antennas that are primarily designed for use on recreational vehicles, and the like. These patents include U.S. Pat. Nos. 5,554,998, 5,528,250, 5,515,065, 5,418,542, 5,337,062, and 4,771,293. The antennas disclosed in these patents have a single main reflector that illuminates a feed horn. These antennas are primarily designed to receive television signals broadcast from a satellite.
U.S. Pat. No. 4,771,293 entitled xe2x80x9cDual Reflector folding Antennaxe2x80x9d discloses a folding antenna for use in a satellite communication system that is used as part of a mobile earth station that is part of a satellite communication system for news gathering purposes. This antenna has a supporting base, a main reflector and a subreflector. The main reflector and subreflector rotate downward toward the base from a deployed position to a stowed position where the two reflectors lie relatively close to the base. The base forms part of a container that encloses the reflectors when in the stowed position. The two reflectors are hinged relative to each other and relative to the base. The two reflectors move from a stowed position where they lie relatively close to the base, to a deployed position where they are relatively spaced from the base.
U.S. Pat. No. 5,554,998 entitled xe2x80x9cDeployable satellite antenna for use on vehiclesxe2x80x9d is typical of the other cited patents discloses a deployable satellite antenna system that is intended for mounting on the roof of a vehicle. The elevational position of the reflector is controlled by a reflector support having a lower portion pivotably attached to a base mounted to the vehicle. The elevational position of the reflector can be adjusted between a stowed position in which the reflector is stored face-up adjacent to the vehicle and a deployed position. The feed horn is supported at the distal end of a feed arm having a first segment attached to the reflector support extending outward between the base and reflector, and a second segment pivotably connected to the distal end of the first segment. The feed horn segments move between an extended position in which the feed horn is positioned to receive signals reflected from the reflector, and a folded position in which the feed horn is positioned adjacent to the reflector. A linkage extends between the base and the second segment of the feed arm causing the second segment of the feed arm to automatically pivot to its folded position when the reflector is moved to its stowed position. The linkage also allows a spring to pivot the second segment to its extended position when the reflector is moved to its deployed position. The azimuth of the antenna can be controlled by rotating the base relative to the roof of the vehicle.
The other cited patents generally relate to deployable satellite antennas that have all the major antenna components (i.e. feed horn assembly, subreflector, main reflector) move independently to deploy and stow the antenna. These other patents are generally unrelated to the present invention.
None of the above-cited antennas are particularly well-suited for use on a spacecraft. Single reflector antennas are typically not used in spacecraft communication systems. The dual reflector antennas disclosed in U.S. Pat. No. 4,771,293, as well as the other antennas, have many moving parts and would therefore be relatively unreliable when used in space applications.
It would be desirable to have a system that improves the ability to store and deploy an antenna system comprising a main reflector and a subreflector that is disposed on a spacecraft. Therefore, it is an objective of the present invention to provide for spacecraft antenna deployment and storage system that stores and deploys an antenna having a main reflector and a subreflector as a single moving assembly.
To accomplish the above and other objectives, the present invention provides for improved systems that are used to store and deploy an antenna disposed on a spacecraft. The antenna comprises an RF feed horn assembly, a main reflector assembly and a subreflector. Alternative embodiments of the present invention package one or two antenna systems each having an RF feed horn assembly, a main reflector assembly and a subreflector.
More particularly, the present invention is a deployable antenna system for use on a spacecraft that is moveable from a stowed position to a deployed position. The antenna system comprises a feed horn assembly comprising one or more feed horns fixedly attached to the spacecraft and a rotatable hinge attached to the spacecraft. A substantially rigid reflector support structure is attached to the hinge that rotates about a hinge axis. The support structure has lower and upper portions. A main reflector assembly (with or without a built-in adjustment mechanism) is attached to the lower portion and a subreflector is attached to the upper portion. The subreflector has a fixed relation relative to the main reflector assembly and is disposed in a fixed relation relative to the feed horn assembly when the antenna system is in the deployed position so that the antenna system generates a predetermined beam coverage pattern.
The present invention provides compact packaging of a spacecraft antenna, especially when the subreflector is relatively large relative to the main reflector. The present invention thus provides for an antenna system having a compact stowage volume. The present invention stows and deploys the main reflector assembly and subreflector as a single unit.
The present invention uses only a single axis deployment mechanism per antenna and deploys the main reflector assembly and subreflector as a single rigid unit. The present invention allows a lightweight, rigid deployment structure being able to provide a smaller misalignment error between the subreflector and main reflector assembly when deployed. The present invention is ideal for deploying an antenna system with a relatively large subreflector, such as a side fed offset Cassegrain antenna, for example, disposed on a side of a spacecraft.
Only one single-axis mechanism is employed per antenna. This is simpler, more reliable and perhaps lighter mass than a two axis mechanism or a dual hinged system such as is disclosed in U.S. Pat. No. 4,771,293, for example. Also there is less pointing error attributed to deployment and thermal distortion due to mismatch of material properties for the present invention. Because of the compact nature of the present invention, it potentially allows a greater number of antenna systems to be disposed on a spacecraft.